An initial report on the 24-hour count that began midnight Monday and ended midnight Tuesday included 233 different species — a drop of 11 from last year when 244 were counted on Mad Island. While the area likely still has one of the United States' most diverse bird populations, the species that were missing raise questions.

Similar changes in bird behavior could be seen this year in the Midwest and parts of the South, areas that have been gripped by a massive drought that covered two-thirds of the nation at its height. The drought's severity is unusual, but scientists warn that such weather could become more common with global warming.